The present invention relates to a method of controlling an engine of a flexible fuel vehicle (FFV) at starting the engine for improving starting characteristics.
Various attempts have been made to provide engine control systems enabling the engine to be operated with alcohol mixed fuel because of energy shortage and improvement of emission control these days. Japanese Patent Application Laid-open 64-69768 discloses one of the systems.
The flexible fuel vehicle having such an engine control system can be driven with gasoline only, or mixed fuel of gasoline and alcohol, or alcohol only. Namely, the concentration of the alcohol in the fuel changes between 0% (gasoline only) to 100% (alcohol only) in dependency on user conditions.
Generally, the alcohol has difficulty in vaporization at a lower temperature and has a higher ignition point compared with the gasoline. If the alcohol concentration changes, the starting characteristics vary a lot in accordance with the temperature. In particular, if the alcohol concentration increases, the starting characteristics lower in a cold engine state.
In order to solve such a problem, a heater or a heating element is provided in the engine to heat the fuel for developing the vaporization of the fuel.
Japanese Patent Application Laid-open 57-52665 discloses a system in which an intake pipe of the engine is heated by a heater controlled in accordance with an output signal of an alcohol concentration sensor. When the alcohol concentration is larger than a reference value, the heating quantity of the heater is increased.
Japanese Patent Application Laid-open 55-35179 discloses a system in which a distributor valve is provided for distributing air-fuel mixture to a main intake passage and a sub-intake passage. A heating element is disposed in the sub-intake passage to vaporize the fuel passing in the sub-intake passage at starting the cold engine.
However, when starting the engine, it is necessary not only to heat the fuel, but also to raise the temperature of a combustion chamber of the engine. For this purpose, it is necessary to enrich the fuel mixture after starting the engine, which causes emission control deterioration and increases fuel consumption.
Furthermore, when starting the engine, the residual fuel in a cylinder or an intake manifold will cause unstable initial combustion.
At low temperature, since the alcohol is easily separated from the gasoline, the distribution of alcohol concentration in the fuel mixture in the fuel tank is not constant. Consequently, the alcohol concentration measured by a concentration sensor is inaccurate, reducing the startability of the engine.
In addition, the vaporization of the fuel is dependent on a heater position in the intake passage. If the healer position is improper, the fuel is incompletely vaporized, so that residual fuel which is not ignited adheres to an inner wall of an intake port. As a result, the air-fuel ratio becomes improper to reduce the starting characteristics and increase the fuel consumption.